This application claims the benefit of Korean Application No. P2001-54123 filed on Sep. 4, 2001, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly, to a method and apparatus for driving a liquid crystal display. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for improving a picture quality.
2. Discussion of the Related Art
Generally, a liquid crystal display (LCD) controls a light transmittance of each liquid crystal cell in accordance with a video signal to thereby display a picture. An active matrix LCD including a switching device for each liquid crystal cell is suitable for displaying a moving picture. The active matrix LCD uses a thin film transistor (TFT) as a switching device.
The LCD has a disadvantage in that it has a slow response time due to inherent characteristics of a liquid crystal such as a viscosity and an elasticity, etc.
Referring to FIG. 1, the conventional LCD cannot express desired color and brightness. Upon implementation of a moving picture, a display brightness BL fails to arrive at a target brightness corresponding to a change of the video data VD from one level to another level due to its slow response time. Accordingly, a motion-blurring phenomenon appears from the moving picture and a display quality is deteriorated in the LCD due to a reduction in a contrast ratio.
In order to overcome such a slow response time of the LCD, U.S. Pat. No. 5,495,265 and PCT International Publication No. WO99/05567 have suggested to modulate data in accordance with a difference in the data using a look-up table (hereinafter, referred to as high-speed driving scheme). This high-speed driving scheme allows data to be modulated by a principle as shown in FIG. 2.
Referring to FIG. 2, a conventional high-speed driving scheme modulates input data VD and applies the modulated data MVD to the liquid crystal cell, thereby obtaining a desired brightness MBL. This high-speed driving scheme modulates input data on the basis of a difference of the data so that a desired brightness can be obtained in response to a brightness value of the input data within one frame interval. Accordingly, the LCD employing such a high-speed driving scheme compensates for a slow response time of the liquid crystal by modulating a data value in order to alleviate a motion-blurring phenomenon from a moving picture, thereby displaying a picture at desired color and brightness.
The high-speed driving scheme compares each most significant bit data MSB of the previous frame Fnxe2x88x921 and the current frame Fn, and selects the modulated data corresponding from the look-up table to modulated as in FIG. 3, if there is any change between the most significant bit data MSB.
In case of limiting the most significant bits to 4 bits, the look-up table of the high-speed driving scheme is implemented as in Table 1 and Table 2.
In Table 1 and Table 2, a furthermost left column is for a data voltage VDnxe2x88x921 of the previous frame Fnxe2x88x921 while an uppermost row is for a data voltage VDn of the current frame Fn. Table 1 is a look-up table information in which the most significant 4 bits (i.e., 20, 21, 22 and 23) are expressed by the decimal number format. Table 2 is a look-up table information in which weighting values (i.e., 24, 25, 26 and 27) of the most significant 4 bits are applied to 8-bit data.
Only the most significant bit data MSB are modulated in order to reduce the memory size and the look-up table upon implementation of hardware. In such a manner, the high-speed driving apparatus may be implemented, as shown in FIG. 4.
Referring to FIG. 4, a conventional high-speed driving apparatus includes a frame memory 43 connected to a most significant bit bus line 42, and a look-up table 44 connected to both the most significant bit bus line 42 and the frame memory 43.
More specifically, the frame memory 43 stores the most significant bit data MSB during one frame interval and supplies the stored data to the look-up table 44. Herein, the most significant bit data MSB are high-order 4 or 3 bits in the 8 bit data as described above.
The look-up table 44 compares the most significant bit data of the current frame Fn inputted from the most significant bit bus line 42 and the most significant bit data of the previous frame Fnxe2x88x921 inputted from the frame memory 43 in Table 1 and Table 2, thereby selecting and outputting modulated data Mdata. The modulated most significant bit data Mdata are added with least significant bit data bypassed through a least significant bit bus line 41, and is then inputted into a liquid crystal display.
Nevertheless, the above high-speed driving method and apparatus still has a problem. For example, a difference between a modulated 8 bit data value and an actual input value becomes great even though there is almost no difference between gray levels, as shown in FIG. 5. In this case, actual gray level values which generally do not cause a recognizable difference to the naked eye. Nonetheless, it causes the recognizable difference in brightness to the naked eye. As a result, a picture quality is deteriorated as much.
FIG. 5 illustrates 8 bit modulated data expressed in decimal number. Each of the most significant bit data MSB is added with the least significant bit data LSB of 4 bits.
In FIG. 5, a band (X,Y) is the value calculated by adding the least significant bits of 4 bits with the most significant bit data MSB of 4 bits that are modulated, and is defined as a modulated data band divided by each most significant bit data MSB. Herein, X represents the value of the most significant bit data MSB of the previous frame Fnxe2x88x921 expressed in 8 bit data, while Y represents the value of the least significant bit data LSB of the current frame Fn expressed in 8 bit data. The data shown in the shadow cell, which are the most significant bits in each band (X,Y), represent the modulated data registered at the look-up table of Table 1 and Table 2.
As described in Table 2 and FIG. 5, the value of the most significant bit data MSB is added with xe2x80x980xe2x80x99 to xe2x80x9815xe2x80x99 corresponding to the value of the least significant bit data LSB of 4 bits, which is added with the most significant bit data MSB modulated at each band of the look-up table.
On the other hand, even when the most significant bit value included at each band of the look-up table is the same, each of the modulated data values from adjacent bands having the same most significant bit value shows a big difference. This is because the modulated most significant bit data MSB are added with the least significant bit data LSB in each band. For example, when a band (32, 0) and a band (32, 16) have the same most significant bit value of xe2x80x980xe2x80x99 in Table 2, the least significant bit data LSB added as in FIG. 5, xe2x80x980xe2x80x99 to xe2x80x9815xe2x80x99 are added according to the value of the least significant bit data LSB thereof. Consequently, when the modulated data are changed from xe2x80x9832xe2x80x99 to xe2x80x9815xe2x80x99 and xe2x80x9832xe2x80x99 to xe2x80x9816xe2x80x99 in the look-up table, a brightness change should not be recognizable to the naked eye. Nonetheless, the brightness change between the corresponding data is recognizable to the naked eye because the modulated data are changed from xe2x80x9832xe2x80x99 to xe2x80x9815xe2x80x99 and xe2x80x9832xe2x80x99 to xe2x80x980xe2x80x99, respectively. This happens particularly at the boundary between the adjacent bands where the modulated most significant bit value is equal, such as between a band (48,0) and a band (48,16), and a band (64,0) and a band (64,16).
Accordingly, the present invention is directed to a method and apparatus for driving liquid crystal display that substantially obviates one or more of problems due to limitations and disadvantages of the related art.
Another object of the present invention is to provide a method and apparatus for driving a liquid crystal display that improves a picture quality.
Additional features and advantages of the invention will be set forth in the description which follows and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a method of driving a liquid crystal display includes dividing input data into most significant bit data and least significant bit data, deriving a data value from modulated data registered in advance for modulating the most significant bit data, determining whether adjacent modulated data are equal to each other, and replacing the least significant bit data with a desired value if the adjacent modulated data are equal to each other.
The method further includes maintaining the least significant bit data without a modulation if the adjacent modulated data are not equal to each other.
The method further includes adding the least significant bit data with the most significant bit data which are modulated to the modulated data to input into a liquid crystal display.
In the method, the modulating the most significant bit data includes determining modulated data in accordance with a difference in the input data between a previous frame and a current frame, matching the modulated data with respect to each band in a look-up table, and searching the band in the look-up table corresponding to the most significant bit data, thereby modulating the most significant bit data using the modulated data of the searched band.
In the method, determining whether adjacent modulated data are equal to each other includes deriving the modulated data from each modulated data of an adjacent band and a selected band corresponding to the most significant bit data, and determining whether the derived adjacent modulated data from each of the adjacent bands are equal.
In another aspect of the present invention, a driving apparatus for a liquid crystal display includes a memory delaying most significant bit data of input data inputted from an input line, a modulator modulating the most significant bit data from the input line and the delayed most significant bit data to select one modulated data among a plurality of modulated data registered in advance, a comparator determining whether the adjacent modulated data are equal to each other, and a least significant bit converter replacing the least significant bit data with a desired value if the adjacent modulated data adjacent are equal to each other.
In the driving apparatus, the least significant bit converter maintains the inputted least significant bit data if the adjacent modulated data are not equal to each other.
The driving apparatus further includes a data driver supplying the modulated data and bypassed data to the liquid crystal display, a gate driver supplying a scanning signal to the liquid crystal display, and a timing controller supplying the input data to the input line, and controlling the data driver and the gate driver.
In the driving apparatus, the most significant bit data and the least significant bit data are added and supplied to the data driver.
In the driving apparatus, the modulator includes a look-up table having the modulated data by bands in accordance with a difference in the input data between a previous frame and a current frame.
The least significant bit converter includes a first inverter inversing an output signal of the comparator, an NAND gate performing an NAND operation on an output signal of the first inverter and least significant bit data from the input line, and a second inverter inversing an output signal of the NAND gate.
In a further aspect of the present invention, a liquid crystal display panel having a plurality of data lines and gate lines and displaying images, a memory delaying most significant bit data of input data inputted from an input line, a modulator modulating the most significant bit data from the input line and the delayed most significant bit data to select one modulated data among a plurality of modulated data registered in advance, a comparator determining whether the adjacent modulated data are equal to each other, a least significant bit converter replacing the least significant bit data with a desired value if the adjacent modulated data are equal to each other, a data driver supplying the modulated data and bypassed data to the liquid crystal display, a gate driver supplying a scanning signal to the liquid crystal display, and a timing controller supplying the input data to the input line, and controlling the data driver and the gate driver.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.